1. Field of the Invention
The present invention relates to a method and apparatus for stripping photoresist from a substrate.
2. Discussion of the Related Art
Generally, a liquid crystal display in flat display panels has the characteristics of low-voltage driving, low power consumption, full-color realization, lightness, compact size, and the like, thereby rendering it widely applicable to a mobile terminal, a notebook computer, a video appliance, and the like.
A liquid crystal display device is fabricated by bonding two substrates having a plurality of patterns formed thereon to confront each other while leaving a predetermined interval therebetween and injecting a liquid crystal material between the two substrates. In this case, a plurality of the patterns are formed by photolithography.
Photolithography is carried out in the following manner: First of all, a photoresist as a photo-reactive material is coated on a layer of a specific material formed on a substrate. The photoresist layer is covered with a mask having a predetermined pattern. Exposure is carried out on the photoresist through the patterned mask. The exposed photoresist transcribes the predetermined pattern of the mask by exposure, and is then developed into a photoresist pattern.
Subsequently, a layer of the specific material is patterned using the photoresist pattern as an etch mask. The photoresist pattern is then removed from the patterned layer of the specific material using a stripper. In this case, the process of removing the photoresist pattern from the layer of the specific material is called a stripping process.
Apparatus corresponding to a process of coating the photoresist on the layer of the specific material, an exposure process of the photoresist, a development process of the photoresist, an etch process of the layer of the specific material, and a stripping process of the photoresist, respectively are in-line.
FIG. 1 illustrates a diagram of an apparatus having etching and stripping modules 42 and 44 for fabricating a liquid crystal display device.
Referring to FIG. 1, the apparatus includes a loader 40 carrying a cassette (not shown in the drawing) containing a plurality of substrates therein for loading the carried substrate in the apparatus: an etching module 42 for etching the respective substrates loaded by the loader 40 with an etchant, a stripping module 44 for stripping the patterned photoresist coated on each of the substrates, which have been etched by the etching module 42, using a stripper, and an unloader 45 for unloading each of the substrates having the patterned photoresist stripped therefrom.
The substrates are conveyed to the unloader 45 from the loader 40 by a conveyer, a robot, or a conveying roller.
In this case, the etching module 42 includes an initial cleaning unit 42a for initially cleaning the loaded substrate, an etching unit 42b for spraying the etchant to etch the layer of specific material exposed between the patterned photoresist, a first cleaning unit 42c for spraying a cleaning agent to remove the reactants produced through the etching process by the etchant, and a first drying unit 42d for drying the cleaning agent.
The stripping module 44 includes a neutral unit 44a transferring the substrate loaded therein by a conveying unit 43 to the stripping module, a stripping unit 44b for removing the patterned photoresist remaining on the substrate, a second cleaning unit 44c for cleaning the substrate having the patterned photoresist stripped therefrom using de-ionized water, an organic solvent, or an inorganic solvent, and a second drying unit 44d for drying the cleaning agent.
The apparatus for stripping the patterned photoresist, as the stripping unit 44b, is explained as follows.
FIG. 2 illustrates a structural diagram of an apparatus for striping photoresist according to a related art.
Referring to FIG. 2, an apparatus for stripping the photoresist according to related art includes a stripper supplying unit 14 containing a plurality of nozzles 15 for spraying the stripper, a conveying roller 12 installed under the stripper supplying unit 14 for conveying the substrate coated with the patterned photoresist 11 from one side to the other side, a bath 13 for collecting the stripper material through the stripping process, a stripper discharging pipe 22 for draining the stripper from the bath 13, a stripper storing unit 21 for maintaining the stripper drained through the stripper discharging pipe 22, and a stripper supplying pipe 16 installed between the stripper storing unit 21 and the stripper supplying unit 14 for supplying the stripper supplying unit 14 with the stripper material stored in the stripper storing unit 21.
In the apparatus for stripping the patterned photoresist according to the related art, once the substrate 10 is loaded in the bath 13 by a driving force of the conveying roller 12, the stripper supplying unit 14 sprays the stripper material on the substrate 10 to strip the patterned photoresist 11 coated on the substrate 10.
A method of fabricating a liquid crystal display device using the apparatus for striping a patterned photoresist according to related art is explained as follows.
FIGS. 3A to 3F illustrate cross-sectional views of a process for fabricating a liquid crystal display device using the method of related art.
Referring to FIG. 3A, a Cr layer 2 is formed with a thickness of 0.2 μm or less on a first substrate 1, and a photoresist 4 as a photo-reactive resin is coated uniformly on the Cr layer 2 by spinning or roll coating.
Referring to FIG. 3B, a photomask 6 having a predetermined pattern is disposed over the photoresist 4. Rays of, e.g., UV-rays in general, electron beams, or X-rays are then applied toward the substrate 1 from the upper side of the photomask 6 to depict a predetermined pattern of the photomask 6 on the photoresist 4. This process is called an exposure process.
Subsequently, the photoresist 4 after the exposure process, is exposed to a high temperature, and ions are implanted in the photoresist 4, or the photoresist 4 is hardened by UV-rays just to increase the anti-solubility of the patterned portion of the photoresist 4.
Referring to FIG. 3C, a process of developing the photoresist is carried out using a developing solution. The remaining portion of the exposed photoresist 4 except the patterned portion is then removed. The process of exposure and development is called a patterning process.
In the case that the photoresist 4 is positive, the portion of the photoresist 4 exposed to the rays is removed. If the photoresist 4 is negative, the portion of the photoresist 4 failing to be exposed to the rays is removed.
Referring to FIG. 3D, the Cr layer is etched by a specific etchant using the patterned photoresist 4 as an etch mask, to form a black matrix 3. In this case, such an etch process can be performed by a dry etch using plasma or a wet etch using a chemical solution.
The black matrix 3 is formed on a part from which current or light leaks, as well as a part failing to control liquid crystal alignment, such as a portion of disclination to cut off light leakage.
Thereafter, the patterned photoresist is completely removed using the stripper, whereby the patterned black matrix 3 remains on the first substrate 1 as illustrated in FIG. 3E.
In this case, the stripper for the patterned photoresist 4 is an organic chemical compound mixed with additives such as NMP (N-methylpyrrolidone), MEA (monoethanolamine), BDG (butyldiglycol), carbitol{2-(2-ethoxyethoxy)ethanol}, a nonion based additive, a fluorocarbon based additive, a silicon based additive, and the like.
In this case, the MEA breaks the cross-linking of the photoresist, the NMP swells the photoresist, the BDG wets the photoresist with a solution, and the carbitol or IPA helps the photoresist dissolve in a solution.
Subsequently, the substrate 1 is cleaned by an organic material in order to prevent corrosion of layers that will be formed later as well as to remove residue of the photoresist 4.
Referring to FIG. 3F, a color filter layer 7 is sequentially formed by sequentially coating a R-color resist, a G-color resist, and a B-color resist between the patterned black matrix 3. ITO (indium tin oxide) as a transparent conductive material and as a common electrode 8 is deposited on an entire surface including the color filter layer 7.
Meanwhile, a gate line (not shown in the drawing) and a gate electrode (not shown in the drawing) are formed by forming a first metal layer of Al or Al alloy on a second substrate and patterning the first metal layer by photolithography. A gate insulating layer is formed by stacking an inorganic insulating layer of SiNx or SiOx on the entire exposed surface, including the gate line, by sputtering.
Subsequently, a semiconductor layer is formed by depositing amorphous silicon on the gate insulating layer over the gate electrode, and a second metal layer of Cr or Mo is formed on the entire surface including the semiconductor layer. The second metal layer is then patterned by photolithography, whereby a data line, a source electrode, and a drain electrode are formed.
Thereafter, a passivation layer is formed with SiNx or SiOx on the entire surface including the data line, and a pixel electrode of ITO penetrating the passivation layer is formed just to be connected to the drain electrode.
In this case, the gate and data lines are arranged to cross with each other, whereby scan and data signals are transferred to the corresponding pixels, respectively. A thin film transistor including the gate electrode, semiconductor layer, source electrode, and drain electrode is formed at each intersection between the gate and data lines. The thin film transistor plays a role in applying a voltage to the corresponding pixel electrode or cutting off the voltage. Each of the pixel electrodes is arranged to confront the corresponding common electrode and plays a role in controlling alignment of liquid crystal molecules.
In order to form the above-mentioned elements, several photolithography processes are carried out. In this case, each of the photolithography processes includes the steps of patterning and stripping the photoresist.
Subsequently, a seal pattern is formed as an adhesive agent on a circumference of the surface of the first substrate, and a spacer is evenly dispersed on the second substrate. The first and second substrates are arranged to confront each other, and then are bonded to each other.
The bonded substrates are cut into unit cells, and then liquid crystals are injected between the two substrates of each of the unit cells through a liquid crystal injection inlet previously formed. Finally, the liquid crystal injection inlet is sealed so that the injected liquid crystals does not leak out. Thus, a liquid crystal display device is completed.
Unfortunately, the related art has the following problems or disadvantages.
First of all, when an organic based solution is used as the stripper for the photoresist, the product cost of the liquid crystal display device increases since an organic based material is expensive.
Secondly, a system for preparing for a possible fire when using the organic based solution is necessary, whereby the apparatus for fabricating the liquid crystal display device become complicated.
Thirdly, in order to overcome the problem of the organic based solution, an inorganic based stripper of KOH can be used. However, the KOH stripper reacts with the photoresist, generating a foam, and further contaminates the fabricating apparatus. Hence, a cleaning process for removing the foam is required, and the time required for conducting the cleaning process extends the overall time of fabrication.
Finally, the endurance of the filter used for reuse of the used stripper material is shortened.